Litebulbs,
you are quoting CAP 371, which is not the relevant document for BA crew, rather you need to look at JPM 1.16. However, I doubt there is little difference in this particular case and I cannot be bothered to look it up. Despite that, you are confusing min rest and a rostered day off. There is no legal requirement to have a rostered day off post a LH trip.
The min rest would be for CC 11 hours or the length of the preceeding duty minus one hour if trhe preceeding duty exceeded12 duty hours. So if the preceeding duty was 13:30 then min rest is 12:30 for CC. A Rostered day off is something else entirely - it is a day clear of duty and must include two locla nights - again there is a definition of a local night that I cannot be bothered to look up but is something like a night with no duty after 22:00 or before 06:00. I am sure someone here will provide chapter and verse on definitions.
There is no legal restriction requiring a day off between LH flights. As Betty Girl has stated this may be legal but as to whether it is desirable is another matter.